Solar project profile and video: 98 kW zero export system

Installing a sub-100 kW system on an unshaded warehouse roof might sound like a relatively straightforward proposition, as commercial solar projects go.

But this project – a 98.28 kW system installed by Queensland Commercial Solar (QCS) for a heavy equipment rental company – is a good illustration of how a few complicating factors can quickly ramp up the complexity of medium-sized solar developments.

After encountering a few hurdles, including some 20-year-old wiring and an isolated electricity meter, the installation ended up with multiple PV arrays, multiple inverters on two buildings, a standalone zero export device and a detailed monitoring system integrated by Wi-Fi and radio. <

As Jimmy Badcock, co-director of QCS, says: “Installing commercial solar is very different to installing residential solar.” He’s not kidding.

In fact, Mr Badcock believes the system design could become a case study for other complex zero export sites. “As far as we’re aware, this is a one of a kind installation,” he says. “The zero export control board is remote from the two inverter sites, and had to be fail safe, as well as provide linear ramping control and eGauge reporting facilities. This overcomes the challenges of installing solar on multiple arrays and inverter banks in different locations all controlled in harmony together.”

Simple motives The final design may be atypical, but, as Mr Badcock explains, the inspiration for the project was entirely straightforward.

“Salmon Earthmoving is a family owned business,” says Mr Badcock. “They want to be seen as clean and green, as well as save money, especially given the introduction of the new kVA-based demand charges in Queensland.”

With these factors in mind, Salmon Earthmoving contacted SmartConsult, a professional consultancy specialising in commercial solar, to investigate the feasibility of putting a system on their head office at Stapylton. SmartConsult in turn got in touch with QCS.

“We’ve completed a number of other large commercial solar installations with SmartConsult,” explains Mr Badcock. “We had the requisite experience for this project, and we were brought in very early in the process.”

QCS proceeded with a technical and financial analysis of the proposed installation, and the results were promising. “The technical analysis worked out to be very favourable,” says Mr Badcock, “Salmon Earthmoving operate a large maintenance base for their earthmoving equipment, warehouse and head office. They have a number of large roof structures facing 160 degrees north, several of which were suitable for a solar installation, and the company’s energy usage profile was a good match for solar.”

And once the RET rebate was deducted from the capital cost, the project proved financially viable too.

Finding the best configuration

QCS obtained the client’s interval data from energy retailer Origin and modelled a number of different sizes and configurations using the Homer Pro Microgrid Analysis Tool, including the potential yield (actual usable power that can be generated and used by self-consumption). The installer then submitted a report to the customer as to the best configuration:

So far, so simple. But, as Mr Badcock explains, that’s when things started to get complicated.

“Energex [the Queensland network operator] initially approved a smaller zero export system than was finally constructed at Salmon, due to potential voltage rise and harmonics issues. This was because the main building at Salmon was constructed some 20 years ago, with 120 mm cable that was undersized for the current consumption.”

To overcome this, and gain approval for a larger system from Energex, QCS designed a split system across two roofs, with two 27.6 kW ABB inverters and two arrays on the main building (252 panels), and a third 27.6 kW ABB inverter and array on a second building (126 panels). To extend the daily solar generation, half of the panels from the final array were installed on tilts to catch the early morning sun. QCS also installed an eGauge prior to system installation to record the data for the test and commissioning report.

Split system

While splitting the system across two buildings allowed for a larger system, it also created some difficulties. “Because the main building and the parts warehouse are 150 meters apart, with the main switchboard in a third location, we faced an issue with the zero export control panel,” says Mr Badcock. “Hard wiring communications was impossible due to the conduits, so we designed a custom solution in conjunction with Peter Britten from Supply Partners. It involved a 433 Hz radio link for the protection relays, and two separate Wi-Fi connections for linear ramping control and real-time data collection using the eGauge. The eGauge is integrated directly into the ABB inverter RS-485 output, allowing for the complete system to be monitored (down to string level if required) plus measuring the grid and net consumption.”

Mr Badcock believes the resulting system is the first zero export system in Australia with complete radio control – and more importantly, it worked. QCS was required to submit a comprehensive test and commissioning report to Energex, and the network operator was satisfied that the voltage rise and harmonics issues had been resolved, and would not upset the network.

“The project is a success, it all works!” says Mr Badcock. “The system was commissioned on 9 July 2015 and as of 9 December 2015 it had generated 85,000 kWh. The power savings are much greater than were promised to the customer. It is a vintage year for solar and the expected solar yield.” <br/> <br/>Such is the success of the project that Mr Badcock feels QCS’s design could become a model for other, similar installations. “The solution could be deployed in similar configurations with other inverter types that need to be integrated and centrally controlled and monitored by a standalone zero export device and network protection system attached to the electricity meter box,” he says. “This is especially suitable for school campuses with multiple roofs and inverter locations, or industrial sites like Salmon with standalone and isolated electricity meters.”